Several industrial laser micromachining or material processing applications, such as metal engraving or memory link repair, require that laser light pulses with specific energy and temporal characteristics be precisely directed to a specific region of interest of a target material. For many applications, the rise-time and fall-time of such light pulses must be relatively short, preferably in the order of a few hundreds of picoseconds. It is also advantageous that the intensity profile of the light pulses be arbitrarily varied over the duration of the pulse, which itself varies depending on the application. By way of example, for memory link repair, the pulse duration is typically of a few tens of nanoseconds, while for metal engraving, it is typically of a few hundreds of nanoseconds. In this context, being able to generate light pulses with some capability for dynamically varying pulse durations with a temporal resolution at the nanosecond scale is certainly desirable. The process of generating short light pulses with controllable duration and controllable temporal intensity profile is commonly known in the art as “pulse shaping”.
Laser micromachining processes usually involve specifically tailored recipes consisting of a sequence of operations in which a large number of light pulses are successively impinged on a piece of material. Such recipes generally require that light pulses impinge on the target material for a given time interval during which the pulse repetition rate, the pulse shape, and sometimes the light wavelength can be dynamically switched among a predefined set of distinct combinations of these parameters. For example, the recipe may require that for a given time interval the optical output be simply turned off. The optical intensity may also be set to oscillate in what is commonly known in the art as a quasi-continuous wave (QCW) mode. A laser system operating in QCW mode typically emits a periodic signal oscillating at a frequency around 100 MHz with a duty cycle around 50%. Such functionalities are illustrated in FIG. 1, where the optical output OPTICAL_OUT, under the action of command signals QCW, EXT_TRIG, and SHAPEA/B, is switched between the above-mentioned modes.
Furthermore, in many situations encountered in automated industrial manufacturing, a laser micromachining apparatus such as the one discussed above may need to operate in concert with other manufacturing equipment. For example, it starts or halts the machining of material pieces under remote control, or it may reply when it is remotely interrogated about the current statuses of its constituent lasers.
From the discussion above, it can be seen that there is a need, at least in the context of industrial equipment, for combining some very low-level, agile and time-critical optical pulse shaping capabilities with electrical and optical power amplification, as well as high-level embedded intelligence for performing system housekeeping and managing communications with other equipment. Furthermore, such capabilities should be as low-cost as possible.
The manner in which pulse shaping is performed may originate from electronic signals, either analog or digital, or from optical ones.
U.S. Pat. No. 7,428,253 (MURISON et al.), entitled “Method and system for a pulsed laser source emitting shaped optical waveforms” presents a wavelength-tunable pulsed laser source with optical pulse shaping based on a digital approach. MURISON mentions that the shaped waveform can originate from a digital pattern stored in memory on-board of a digital-to-analog converter (DAC). However, no embedded hardware implementation of digital pulse shaping is disclosed, except for the use of an off-the-shelf laboratory instrument such as the AWG2040 (tradename) waveform generator from Tektronix Inc., (Beaverton, Oreg.).
U.S. Pat. No. 8,073,027 (DELADURANTAYE et al.), entitled “Digital laser pulse shaping module and system” discloses a standalone embedded laser micromachining instrument based on digital pulse shaping. As shown in FIG. 2A (PRIOR ART), the instrument includes an input/output (I/O) port for interfacing with external equipment, a communication port for interfacing with a remote computer, a microcontroller for system housekeeping and control of pulse shaping, the digital pulse shaping sub-system and DAC, electrical power amplification and, finally, a laser oscillator for emission of the temporally-shaped output pulses. The electronic QCW/pulse shaping module shown in FIG. 2A is further detailed in FIG. 2B (PRIOR ART). It uses double-data rate (DDR) data output and is implemented preferably in a high-end Virtex-2 Pro FPGA (tradename) from Xilinx Inc., (San Jose, Calif.) in order to generate 10-bit pulse shapes with a typical temporal resolution of 2.5 ns. DELADURANTAYE also describes how the electronic pulse shaping system can be connected to several configurations or architectures of laser oscillators.
U.S. Pat. No. 7,813,389 (PENG et al.), entitled “Generating laser pulses of prescribed pulse shapes programmed through combination of separate electrical and optical modulators” discloses a pulse shaping approach based on superposing delayed analog electrical pulses. It also points out that a fully digital approach equivalent to their analog approach can be implemented using remote computer interfacing, programmed control, digital shaping, a DAC and power amplification. This is illustrated in FIG. 2C (PRIOR ART). PENG also suggests that the digital pulse shaping can be implemented in an FPGA such as the high-end Virtex-5 (tradename) from Xilinx Inc.
The above-mentioned references teach that digital pulse shaping is preferably implemented using high-end, expensive FPGAs, therefore contributing significantly to the high cost of laser micromachining instruments. There is therefore a need for less expensive alternatives for implementing digital pulse shaping.